Crystal structure of a hydrogen sulfide sorption complex of fully Ca2+-exchanged zeolite X

Abstract

Abstract The crystal structure of a hydrogen sulfide sorption complex of dehydrated fully Ca 2+ -exchanged zeolite X, Ca 46 Si 100 Al 92 O 384 ·ca. 149H 2 S [ a =24.864(5) A], has been determined by single-crystal X-ray diffraction methods in the cubic space group Fd 3 at 21(1)°C. A crystal of Ca 46 -X was dehydrated at 380°C and 2×10 −6 Torr for two days, followed by exposure to 200 Torr of dry hydrogen sulfide gas at 21(1)°C. The structure was determined in this atmosphere and was refined to the final error indices R 1 =0.073 and R 2 =0.067 with 407 reflections for which I >3 σ ( I ). In this structure, 16 Ca 2+ ions per unit cell fill site I at the centers of the double six-rings, and the remaining 30 are at site II in the supercages. All 46 are octahedral. Each site-II Ca 2+ ion is recessed 0.84 A into the supercage from the plane of the three oxygens to which it binds [Ca–O=2.373(9) A] and coordinates at 3.12(3) A to three H 2 S sulfur atoms in the supercage. Each of the remaining ca. 59 H 2 S `hydrogen bonds' to two 12-ring oxygens [S–O=3.27(6) A and O–S–O=95.6(13)°], (nearly) filling all 12-rings with four H 2 S molecules each. The H 2 S molecules have not dissociated upon sorption.